Motor Inrush Current Calculator
Calculate the peak inrush current for AC motors
Motor Inrush Current Calculator
Compliant with NEMA MG 1 Standards
Results:
Peak Inrush Current (A): 0.00
How to Use the Calculator
AC Single Phase Motor
- Select "AC" system type
- Choose "Single Phase"
- Enter Motor Full Load Current (FLA) in Amps
- Input the Inrush Multiplier (typically 6-8)
AC Three Phase Motor
- Select "AC" system type
- Choose "Three Phase"
- Enter Motor Full Load Current (FLA) in Amps
- Input the Inrush Multiplier (typically 6-8)
DC Motors
- Select "DC" system type
- Note: Inrush current calculation is not applicable in the same way for DC motors.
- Starting current for DC motors is primarily limited by winding resistance.
Motor Inrush Current Fundamentals
AC Motor Inrush
When an AC motor starts, it draws a significantly higher current than its full load current for a brief period. This "inrush current" is due to the motor's low impedance at startup and can be 5 to 10 times the motor's rated current.
- Causes: Low rotor speed, magnetic saturation
- Effects: Voltage dips, nuisance tripping of protective devices
- Duration: Typically a few cycles to several seconds
DC Motor Starting Current
- For DC motors, the initial current is limited by the armature winding resistance.
- Starting current can be high if not limited by external resistance or control.
- Not referred to as "inrush" in the same context as AC motors.
Key Formula:
Inrush Current (A) = Motor Full Load Current (FLA) (A) × Inrush Multiplier
Calculation Formulas
AC Motors:
Inrush Current (A) = FLA (A) × Inrush Multiplier
DC Motors:
Starting Current (A) = Voltage (V) / Winding Resistance (Ω)
Note: The DC formula is a simplified view; actual starting current depends on motor design and control.
Example Calculation
Three Phase AC Motor:
Motor Full Load Current (FLA): 50 A
Inrush Multiplier: 7
Inrush Current = 50 A × 7 = 350 A
Peak Inrush Current = 350 A